1. Field of the Invention
The present invention relates to an image processing apparatus including an image pickup system and compression processing means for compressing a photographic image obtained from the image pickup system.
2. Description of the Related Art
FIG. 1 is a schematic block diagram showing the arrangement of a conventional example in which a video camera is integrated with a digital video tape recorder for digitally recording a video signal.
In the example shown in FIG. 1, an image-pickup device 10 is provided with a complementary color filter and performs pseudo-interlaced reading of electric charge stored by field storage. Specifically, as shown in FIG. 2, the image pickup device 10 is provided with a mosaic color filter made up of filter elements: white (W), cyan (Cy), yellow (Ye) and green (G). The image pickup device 10 outputs the added values of two adjacent upper and lower lines, and a luminance signal processing circuit 12 adds together the values of two adjacent pixels contained in the output of the image pickup device 10, thereby forming a luminance signal. A chrominance signal processing circuit 14 obtains differences between the values of the two adjacent pixels, thereby forming color-difference signals.
More specifically, a luminance signal Yn obtained from a line #n and a luminance signal Yn+1 obtained from a line #(n+1) are as follows:Yn=(W+Cy)+(G+Ye)Yn+1=(W+Ye)+(G+Cy)and the associated chrominance signals Cn and Cn+1 are as follows:Cn=(W+Cy)−(G+Ye)Cn+1=(W+Ye)−(G+Cy)
If the characteristic of each filter element W is equal to the sum of R (red), G (green) and B (blue), i.e., R+G+B; the characteristic of each filter element Cy is equal to B+G; and the characteristic of each filter element Ye is equal to Ye=R+G, the following equations are obtained:Yn=Yn+1=2R+4G+2BCn=2(B−G)Cn+1=2(R−G)
As shown in FIG. 2, the line numbers of adjacent upper and lower lines to be added together are made to differ between an even field and an odd field, whereby an interlaced signal is obtained. To perform this addition, the image pickup device 10 needs to be provided with a photoelectric conversion element having lines the number of which is equivalent to the number of lines per frame (in the NTSC system, 525 lines). In the case of the NTSC system, in a line Lm of the image pickup device 10 shown in FIG. 1, m is 525.
A luminance signal Y formed by the luminance signal processing circuit 12 and a chrominance signal C formed by the chrominance signal processing circuit 14 are stored in an image memory 16 under the control of a memory control circuit 18. When image data for one frame are stored in the image memory 16, a motion detecting circuit 20 discriminates between a moving image portion and a still image portion. An image compressing circuit 22 compresses the image data supplied from the image memory 16, by using correlations present in the image. At this time, the image compressing circuit 22 adaptively switches compression algorithms between the still image portion and the moving image portion in accordance with the detection result provided by the motion detecting circuit 20.
The compressed image data is applied to an image recording device 24, and the image recording device 24 records the compressed image data on a recording medium.
A system control circuit 26 controls the entire arrangement in accordance with the operation of a key operation device 28.
In the above-described arrangement, pseudo-interlaced field images are compressed and recorded on the recording medium.
In the conventional example in which compression processing is performed after field images are combined into a frame image, there is the problem that if field images of a fast moving subject are combined into a frame image, the resultant image may be blurred as shown in FIGS. 3(a) to 3(c). FIG. 3(a) shows an odd field image, FIG. 3(b) shows the succeeding even field image, and FIG. 3(c) shows the frame image obtained by combining the odd and even field images.
Compression of an image utilizes correlations which appear in the image in the space and time-axis directions thereof. In general, a frame picture the vertical line-to-line distance of which is smaller than that of a field picture contains higher correlations. For this reason, as described above, the conventional example adopts the compression method of adaptively switching compression algorithms between a still image portion and a moving image portion in a frame image.
As a result, the conventional example necessarily needs a motion detecting circuit for detecting a still image portion and a moving image portion, and, in addition, a substantially high detection accuracy is needed. This problem makes it difficult to reduce the size of the circuit.
As is known to those skilled in the art, since a conventional camera-integrated type of VTR does not conform to a plurality of television standards, a plurality of camera-integrated types of VTRs must be prepared and selectively used according to individual purposes. With the diversification of broadcasting systems, it becomes far more necessary to exchange program software tapes between different nations or to produce software conforming to multiple broadcasting systems. However, if a plurality of broadcasting systems are to be handled, a plurality of existing VTRs are needed, so that practical inconveniences will be encountered. For this reason, it has been desired to provide a VTR unit capable of conforming to multiple broadcasting systems.
As is also known to those skilled in the art, systems for recording and reproducing a digitized video signal are individually designed according to necessary image qualities or recordable/reproducible-data rates. However, if system designs differ in coding sampling frequency which is a primary parameter for determining image quality, when one system is connected to another video system, various problems occur.
Such conventional systems which are separately designed according to individual required image qualities have the problem that it is impossible to readily exchange image data between systems via media.